Supporters of the proposed Internet sales tax like to make it sound as though they just care about the little guy, the shopkeeper still intrepid enough to keep the doors open at her bricks-and-mortar store on Main Street. And in fact, the matching bills in the House and Senate -- which would require online retailers to collect sales tax on all transactions and hand the money over to state and local governments -- are called the Marketplace Fairness Act. But, like many things in Washington, especially those that suddenly start to move through Congress quickly, very big business has thrown its weight behind the proposal.